How to hide an image using transparent rectangle in QML?

问题

In the below code I want to hide the image using transparent rectangle. Please give me some solutions. I have used z value but it is not working. The image is still visible.

main.qml

import QtQuick 2.5
import QtQuick.Window 2.2

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")


    Image
    {
        id:underlyingImage
        width: 400
        height: 400
        x:0;
        y:0;
        source:"qrc:/Jellyfish.jpg"
        z:1
    }
    Rectangle
    {
        id:hiding_rect
        width: 400
        height: 400
        x:0;
        y:0;
        color:"transparent"
        z:100
    }
}

回答1:

You can use the OpacityMask to achieve what you try, in the following example we hide a quadrant of the image.

import QtQuick 2.5
import QtQuick.Window 2.2
import QtGraphicalEffects 1.0

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")


    Image
    {
        id:underlyingImage
        width: 400
        height: 400

        fillMode: Image.PreserveAspectCrop
        layer.enabled: true
        layer.effect: OpacityMask {
            maskSource: hiding_rect
        }

        source:"qrc:/Jellyfish.jpg"
    }
    Rectangle
    {
        id:hiding_rect
        width: underlyingImage.width/2
        height: underlyingImage.height/2
    }
}

回答2:

There is another way to use OpacityMask, but your Qt version should be >= 5.7.

import QtQuick 2.0
import QtQuick.Window 2.0
import QtGraphicalEffects 1.0

Window {
    width: 1280
    height: 800
    visible: true

    Rectangle {
        id: background
        anchors.fill: parent
        color: "black"
    }

    Image {
        id: underlyingImage
        width: 1204
        height: 682
        visible: false
        source: "qrc:/timg.jpg"
    }

    Item {
        id: hidingRect
        anchors.fill: underlyingImage
        visible: false

        Rectangle {
            width: underlyingImage.width / 2
            height: underlyingImage.height / 2
            color: "yellow"
        }
    }

    OpacityMask {
        anchors.fill: underlyingImage
        source: underlyingImage
        maskSource: hidingRect
        invert: true
    }
}

The result

来源：https://stackoverflow.com/questions/44165697/how-to-hide-an-image-using-transparent-rectangle-in-qml